1. Field of Invention
The present invention relates to a progressive multifocal ophthalmic lens.
2. Description of Related Art
An ophthalmic lens is a lens worn on a cornea or in an eye for correcting the power of a patient with ametropia. For a patient with an astigmatism, myopia, or hyperopia, wearing an ophthalmic lens should correct both ametropia and astigmatism simultaneously. However, due to the directional ability of an astigmatic eye, an astigmatic ophthalmic lens has a fixed axis relative to the eye, such that an astigmatic ophthalmic lens worn by the patient must have a stabilization design to prevent it from rotating. The stabilization design may cause increased lens thickness, which often results in low oxygen-permeability, high abnormal sensation, or low wearing comfort, or may require more time to be stable. Moreover, the ophthalmic lens needs to be prescribed again if the axis of the ophthalmic lens over shifts relative to the astigmatic axis of the eye. Manufacturing companies must therefore prepare at least 18 different ophthalmic lenses with a single power and 18 axes from 0 degrees to 180 degrees. These ophthalmic lenses require significant inventory, and create increased management pressure, both of which are inconvenient for manufacturing companies.
Moreover, most of the presbyopia lenses on the market are aspherical designs with axis symmetry and progressive power, or are concentric design with alternate distance- and near-visual segments. These two designs primarily dependent on the size of the pupil. Since the size of the pupil changes with the ambient light intensity, contrast, or ages of the patient, and the size-adjustment ability of the pupil decreases as the wearer's age increases, it becomes more difficult to adjust the pupil size for converting between the distance-vision and the near-vision, especially for an eye with huge difference between the ability to see near or far.